A L GA E. SIPHONEAE. 



plant prepares for sexual reproduction, which comes to pass in a peculiar manner. A 

 large number of thick-walled ellipsoidal spores are formed in the compartments of the 

 cap, usually about one hundred on an average in each of the eighty compartments, 

 eight thousand therefore in all. A cir- 

 cular discoid portion of its membranous 

 wall with introverted margin covers one 

 end of the ellipsoidal spore, like a lid 

 pushed too far into a circular aperture, 

 and immediately beyond its inwardly 

 projected edge a delicate ring of ra- 

 diating striae passes through the entire 

 thickness of the wall from within out- 

 wards. The area of wall-membrane 

 thus sharply defined is afterwards cut 

 off as a lid. Numerous swarm-cells, 

 which are in fact gametes^ are pro- 

 duced in the spores. The lid of the 

 spore being removed, the gametes are 

 set at liberty, but they conjugate only 

 when two different spores open at the 

 same time ; there is therefore a sexual 

 difference between the individual spores 

 or sporanges, though there is no ex- 

 ternal indication of this difference. As 

 a rule only two swarm-cells conjugate, 

 but clusters of conjugating organisms 

 are also not infrequent. The zygospore 

 becomes invested with a cell-wall and 

 passes into the resting stage. In ger- 

 mination a unicellular shoot is form- 

 ed with one extremity narrowed and 

 conical, the other broader and rounded ; the latter is the base, the former the apex 

 of the young plant which grows into a tube at first without a cap. The formation of 

 the cap is always preceded by the production of some whorls of branched rays. 



The development of Botrydium * agrees with that of Acetabularia in the circum- 

 stance that spores are formed inside the mother-plants, and that the spores produce 

 motile gametes. Botrydium also possesses the power of asexual multiplication in a 

 remarkable variety of ways. The little plants can become zoosporangia in almost every 

 stage of their existence and produce swarm-spores, which are distinguished from the 

 gametes by having only one cilium. If the plantlets are in danger of being dried up, 

 the whole of the protoplasmic contents migrates into the root-system and fragments 

 into a number of portions which are separated from one another by cell-walls. Each 

 of the cells thus formed can either behave as a zoosporangium, or germinate and pro- 

 duce a tube which grows into a young Botrydium, a proceeding which cannot here be 

 described in detail. 



Isogamous reproduction has also been ascertained in Dasycladus 2 . In this case the 

 gametes are formed in sporangia, which arise in the place of one of the terminal 

 rays of the verticillate branches, which are themselves also again branched. Only 

 those gametes conjugate, according to Berthold, which come from different plants, so 

 that a difference of sex appears to be indicated in this case also in the plants them- 

 selves, or in all the sporanges of a plant. 



FIG. 13. Halimeda Opnntia. 

 basal portion formed of interwoven I 



A thaflns (nat. size) without the 

 meiits ; it is made up of separate 



members which spring from one another as in an Opuntia. K part of 

 a longitudinal section ; the thallus consists of the ramifications of a 

 tube. 



1 Rostafinski u. Woronin, Ueber Botrydium granulatwn (Bot. Zeit. 1877, p. 649). 



2 Berthold in Bot. Zeit. 1880, p. 648. 



